Preparation and characterization of lithium thio-germanate thin film electrolytes grown by RF sputtering for solid state Li-ion batteries

In this study, lithium thio-germanate thin amorphous films were prepared as electrolytes for lithium rechargeable batteries by RF sputtering deposition in Ar atmosphere. The targets for RF sputtering were prepared by milling the appropriate amounts of the starting materials in the nLi2S+GeS2(n = 1, 2, and 3), Li2GeS3, Li4GeS4 and Li6GeS5, binary system. The ~1 μm thin film electrolytes were grown onto a variety of substrates using 50 W power and 25 mtorr gas pressure. Films were sputtered in inactive Ar atmospheres. IR, Raman spectroscopy and XRD were used to characterize the chemical bonding and the local structures in the films. XPS spectroscopy was used to further characterize the composition and electronic structures of the films. Ionic conductivity measurements of the electrolyte film using impedance spectroscopy were used to examine the Li2S dependence of the conductivity. The conductivities of the thin films at 25 C is 1.7 × 10 (S/cm). This ionic conductivities of the thin films are two order magnitude higher than oxide thin films (LiPON) which are commercial thin film electrolytes. Therefore, lithium thio-germanate thin film electrolytes are very promising materials for use Li-ion batteries.